This invention relates to apparatus for inspecting manufactured parts or workpieces, and more particularly to an improved substage illuminator for producing acurate profiles or silhouettes of such parts for gaging or measuring purposes.
When using optical techniques to measure manufactured objects, whether employing visual or automated video methods, a magnification system is used to produce an enlarged image for evaluation. However, the means by which the object is illuminated can have very serious effects on the reliability of such measurements. For example, it is quite commonplace to utilize some form of substage illumination to produce a profile or silhouette of an object that is to be evaluated. If the object is examined on a typical diffuse-illumination light table which utilizes an array of fluorescent lights below a diffusive white glass, the image of the true edges of an inspected object are often confounded by scattered illumination. For example, when examining a cylindrical or spherical object, distorted images of the illuminated surfaces are reflected off the sides of the object, thus producing erroneous results.
To control this undesirable scattering of light, the so-called wall-effect problem, it has become customary to employ substage illumination which is collimated at least to some degree. In other words, the substage illuminator should provide illumination with sufficient angular range to fill the entrance pupil of the imaging optics, and be uniform over the measurement field. Also in some cases it may be necessary to move the optical system relative to the light table in order to inspect a large measurement area of the work or part that is being examined, so that properly maintaining registration of the substage light source with the imaging optics can be problematical.
It is an object of this invention, therefore, to provide an improved, colliimated substage illuminator, which is capable of illuminating a very large area, and which substantially eliminates the wall effect problem which was present in prior such illuminators. Still another object of this invention is to provide an illuminator of the type described which is capable of covering a very large area with collimated light beams capable of producing uniform illumination over a large measurement field.
Another object of this invention is to provide a substage illuminator having a large array of collimated light sources positioned beneath a light table and operative to direct collimated light beams through an adjacent beamsplitter or filter which eliminates dark zones between adjacent light sources.
Still another object of this invention is to provide an improved illuminator that does not have to be adjusted or repositioned, even though the imaging optics may have to be moved in order to inspect a very large area.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.